Heathrow to Luton sees its heaviest traffic on weekday mornings and early evenings, when the M4, A4 and M25 are shared between commuters and airport travellers. If your journey falls in one of those windows, building in some extra time is sensible; outside them, and at weekends, the roads are typically quieter. Either way, the route is planned around the traffic on the day, not around a fixed schedule that ignores it.
We confirm where your driver will meet you well before travel day, and for airport connections the flight is tracked so the pickup follows your actual landing time. The normal airport routine still sits either side of the drive — check-in and security if you are departing, passport control and baggage reclaim if you are arriving — and both are covered by the waiting time built into the fare.
A quick note on group size and luggage at booking saves any surprise on the day: a saloon is comfortable for four with two large cases, and an estate, MPV or 8-seater takes the extra bags, buggies or kit that a bigger trip brings. Since school holidays and summer tend to be busier for journeys like this, booking a little ahead makes securing the right vehicle straightforward.